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    <title>Document</title>
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<body>
    <script>
       /* 
       算数计算中
       +
       作用：拼接符
       只要一边的值为字符串，那么结果就是字符串
        */
        var a ="10";
        var b ="50" ;
        var c = 40;
        console.log(a+b);//1050 灰色 字符串
        console.log(b+c);//5040 
    </script>
</body>
</html>